In UV-curing industry it is well known that the following three aryl hydroxyketone compounds 1-3 are very important photo-initiators for UV-radiation photopolymerizations of olefinically unsaturated systems.
Compound 1: 2-hydroxy-2-methyl-1-phenyl-1-propanone, its CAS number is 7473-98-5.
Compound 2: (1-hydroxycyclohexyl)phenyl-methanone, its CAS number is 947-19-3.
Compound 3: 2-hydroxy-1-(4-methoxyphenyl)-2-methyl-1-propanone, its CAS number is 15482-17-4.
Traditional production processes for compounds 1-3 involve so-called Friedel-Crafts reactions, which typically employes excess anhydrous Lewis acid AlCl3 and highly toxic Cl2 gas as key raw materials, thereby incuring the generations of massive amounts of solid wastes and acidic and basic by-products. Not surprisingly, such technologies are now experiencing increasingly stringent environmental protection pressure. Patent applications US2009/0018354A1 and US2005/0203315A1 had each disclosed new preparation methods for compounds 1-3 through oxidizing their corresponding aryl 1,2-diol precursors. Unfortunately, the oxidants they employed are such heavy-metals as Pd and Cu and their relevant complexes, which are not only prohibitively costly, but also difficult to access and labile for incurring heavy-metal-related environmental pollutions. Thus, there exists a strong need for developing truly “green” and economically sounding production methods for compounds 1-3.
The present invention has now for the first time disclosed that, surprisingly, compounds 1-3 can be simply prepared by oxidizing their corresponding aryl 1,2-diol precursors with Br2 as the oxidant; or alternatively, with Br2 as the oxidation catalyst in conjunction with H2O2 (hydrogen peroxide) as the terminal oxidant. The significant advantages of this invention over the previously known methods are high product yields, economical competitiveness, and environmental friendliness.